The present invention relates to a silane-modified oxidic or siliceous filler, a process for its production and its use.
The treatment of oxidic or siliceous compounds with organosilicon compounds in order by this treatment to strengthen the bond between the inorganic filler and the organic polymer used in filler-reinforced elastomers and thereby to improve the properties of the fillers in the polymers is known.
It is known from DE 2141159, DE 2212239 and U.S. Pat. No. 3,978,103 that sulfur-containing organosilicon compounds, such as bis-(3-triethoxysilyipropyl) tetrasulfide or 3-mercaptopropyl triethoxysilane, are used as the silane coupling agent or reinforcing filler in oxidic-filled rubber compounds, inter alia for tire treads and other parts of car tires.
In order to circumvent the considerable problems that arise during the processing of mercaptosilanes, such as pre-scorch, scorch and plasticity properties for example, it is known that mostly polysulfidic organosilanes, such as for example bis-(3-triethoxysilylpropyl) tetrasulfide or bis-(3-triethoxysilylpropyl) disulfide (DE 2542534, DE2405758, DE19541404, DE19734295), which for silica-filled vulcanizates represent a compromise in terms of vulcanizing safety, simple production and reinforcing performance, can be used as a coupling agent for tire components.
The known incorporation of the corresponding additives, especially organosilanes and the unmodified fillers, into the unvulcanized polymer blends can be performed in various ways.
The in-situ method involves a joint process for mixing fillers, such as carbon black and silica, with organosilanes and the polymers used.
The ex-situ method involves modifying the filler with the corresponding organosilane or a mixture of various organosilanes, before the filler is processed with the polymer to form the unvulcanized rubber mix.
Also known is the addition of organosilanes in liquid form (U.S. Pat. No. 3,997,356) during production of the unvulcanized mix for rubber compounds or the addition of the active filler via a physical mixture of organosilane and filler prepared in advance (DE 3314742, U.S. Pat. No. 4,076,550). The disadvantage of these mixtures, which have undergone no thermal pretreatment, is the poor storage stability and hence the often inadequate property stability of the products.
U.S. Pat. No. 4,151,154 describes oxidic siliceous fillers whose surface is treated with two different types of organosilicon compounds. The oxidic particles are treated in such a way that they display a greater affinity to water and can also be dispersed more easily in aqueous systems.
The modification of kaolin suspended in water with various organosilanes is known from U.S. Pat. No. 3,567,680. However, the organosilicon compounds that are described are water-soluble in the quantities required for modification, such that in this case the filler can be treated from an aqueous solution.
U.S. Pat. No. 4,044,037 describes aryl polysulfides and mineral fillers treated with these compounds, which are used in rubber compounds. They are produced in an aqueous/alcohol formulation containing 80 to 99.9 wt. % alcohol.
A process is also known from EP 01 26 871 wherein the surface of siliceous fillers is modified with the aid of an aqueous emulsion of water-insoluble organosilicon compounds.
It is known that the surface of fillers can be modified by dissolving the organosilicon compound in an organic solvent with subsequent treatment of the fillers, e.g. clays (U.S. Pat. No. 3,227,675).
The known processes for modifying fillers for rubber and plastic applications with surface-active organosilanes or mixtures thereof have the disadvantage of being based on the use of water, organic solvents or direct spraying of the organosilicon compound onto the surface of the filler with a subsequent heat treatment, the conditioning reaction. The known water-insoluble rubber-typical organosilanes can often be effectively chemically bonded with fillers only in hydrocarbon-based solvents, most of which are toxic and readily flammable.
The known fillers modified ex situ with organosilanes have the disadvantage that until now the rubber properties have tended to be not better but in fact poorer than is the case with fillers and silanes mixed together in situ.
In addition, in the case of fillers having a large specific surface area or a pronounced surface texture, silanization is often not homogeneous. Diffusion of the silane molecules into underlying layers of highly porous fillers, such as precipitated silicas for example, can be achieved only incompletely if at all with the modification methods known until now. Macroscopically preformed fillers are therefore modified only inadequately and incompletely by the known silanization processes.
In addition, preformed fillers cannot be silanized successfully and non-destructively or with low abrasion by means of the known silanization processes and the subsequent drying process that is often necessary. The structure of preformed fillers is or would be destroyed or damaged with the known processes (U.S. Pat. No. 4,151,154; DE 3314742 C2; U.S. Pat. No. 3,567,680). Thus, for example, silica granules formed on rolls (DE 3014007) are very rapidly broken down into a poorer quality silica powder (higher dust and fines content) by being introduced into a mixer or similar equipment and kept in motion for an extended period of time.
A process for reacting at least one biopolymeric, biooligomeric, oxidic or siliceous filler in a compressed gas with at least one silane is known from DE 10122269.6.
The use of powdered and granular fillers therein described is disadvantageous. Powdered silicas are disadvantageous in industrial conditions, for example because of their high dust content, low bulk density, poor flow properties and hence commonly poor meterability. Granules can subsequently be obtained from powdered silicas by mechanical compaction. Since this means an additional processing step, manufacturers try to avoid such processes due to economic considerations. These granules easily break down again into the powdered starting material under mechanical loading and in addition the applicational properties of the silicas frequently deteriorate due to the subsequent granulation and associated mechanical loading of the particles.
An object of the present invention is to produce a low-dust silane-modified oxidic or siliceous filler directly from a low-dust microbeaded or microgranular, oxidic or siliceous filler. The silane-modified oxidic or siliceous filler should display a satisfactory, quantitatively easily variable coverage with the corresponding rubber-reactive silanes and, in addition, comparable or better properties than known silane-filler mixtures produced in situ and, in addition, better rubber properties in the rubber than known silane-filler mixtures produced ex situ.
A further object of the invention is to be able to work or process the microbeaded or microgranular, oxidic or siliceous filler to be modified in a low-dust supply form. The external, macroscopic shape of these preformed microbeaded or microgranular, oxidic or siliceous fillers should be largely maintained during the modification process. A largely dust-free or low-dust silane-modified oxidic or siliceous filler should be obtained.
A still further object of the present invention is to provide a process for modifying microbeaded or microgranular, oxidic or siliceous fillers with silanes, wherein the modification reaction is not performed in water or organic solvents.
Yet another object of the present invention is to provide a variety of products containing the low dust silane modified oxidic or siliceous filler described herein.